This application is based on Japanese Patent Application 2000-260984, filed on Aug. 30, 2000, the entire contents of which are incorporated herein by reference.
A) Field of the Invention
The present invention relates to an edge emission type semiconductor device, its manufacture method, and a spatial optical communication device, and more particularly to an edge emission type semiconductor device for emitting super luminescent light (SL light), its manufacture method, and a spatial optical communication device using such a semiconductor device.
B) Description of the Related Art
Super luminescent diodes (SLD) have been studied for applications to semiconductor optical amplifiers and optical fiber gyro power sources. Light output from SLD has low coherence. The operation of SLD relies upon suppression of laser oscillation. However, SL light is emitted via a waveguide having a light gain so that it can be modulated at high speed. From this reason, SLD has drawn attention in terms of a high-speed spatial optical communication element. As a method of suppressing laser oscillation, a method of lowering a reflectivity at both edges of a waveguide, a method of partially forming a light absorption region in a waveguide, and other methods have been proposed.
Both edges of a waveguide are coated with antireflection material in order to lower a reflectivity at both the edges. However, it is difficult to manufacture a high output SLD by lowering the reflectivity to 1xc3x9710xe2x88x925 or smaller. This method is therefore not practical. SLD partially formed with a light absorption region absorbs about a half of the energy of light radiated in a luminescent layer. This poses a problem of a lower luminescent efficiency and heat generation by light absorption. In addition, the element becomes long.
It is an object of the present invention to provide an edge emission type semiconductor device capable of obtaining a relatively large light output without lowering the luminescent efficiency, and its manufacture method.
It is another object of the present invention to provide a spatial optical communication device using such an edge emission type semiconductor device.
According to one aspect of the present invention, there is provided an edge emission type semiconductor device, comprising: a substrate having first and second edges disposed in parallel with each other and a principal surface connecting the first edge with the second edge; an active layer formed on the principal surface and made of semiconductor material radiating light upon injection of carriers; a ridge-like region disposed on the active layer along a path interconnecting a point on the first edge and a point on the second edge, the ridge-like region being made of semiconductor material having a refraction index smaller than a refraction index of the active layer, the ridge-like region defining a waveguide, the path being disposed along the principal surface and including a first region on the side of the first edge and a second region on the side of the second edge, at an intersecting point of the first region and the first edge, a first angle being taken between a normal to the first edge directing toward the principal surface and the first region, and at an intersecting point of the second region and the second edge, a second angle smaller than the first angle being taken between a normal to the second edge directing toward the principal surface and the second region; and electrodes for injecting current in a region of the active layer along the path.
Since the first region is slanted from the normal to the first edge, the components of light are small, which light propagates toward the first edge along the path along the ridge-like region and is reflected at the first edge and returned to the path. It is therefore possible to suppress laser oscillation. SL light is radiated from the first edge. Since the second angle is smaller than the first angle, more components of light reflected at the second edge return to the path. It is therefore possible to suppress unnecessary radiation from the second edge and increase the intensity of SL light to be radiated from the first edge.
According to another aspect of the present invention, there is provided a spatial optical communication device comprising: the edge emission type semiconductor device; and a light receiving device for receiving light radiated from the first edge of the edge emission type semiconductor device.
Spatial optical communication is performed by using SL light. As compared to using luminescence by LED, transmission at higher speed is possible.
According to another aspect of the present invention, there is provided a method of manufacturing an edge emission type semiconductor device, comprising: when setting two cleavage directions to X- and Y-directions of a surface of a semiconductor substrate and considering a plurality of first virtual straight lines disposed in parallel to the Y-direction and spaced by some distance from each other along the X-direction and a plurality of second virtual straight lines disposed in parallel to the X-direction and spaced by some distance from each other along the Y-direction, a step of forming a waveguide structure for propagating light along a plurality of paths parallel to the surface of the semiconductor substrate, each of the plurality of paths being disposed between two adjacent first virtual straight lines, the path having a pattern of first and second regions alternately disposed along the Y-direction, the first region being slanted relative to the Y-direction and the second region being parallel to the Y-direction, and each of the first and second regions crossing the second virtual straight line; a step of forming grooves in the surface layer of the semiconductor substrate along the first virtual straight lines; a step of cleaving the semiconductor substrate along the second virtual straight lines; and a step of further cleaving the cleaved semiconductor substrate along the grooves.
Since the linear first and second regions cross the second virtual straight lines, a high position precision is not necessary when cleavage is performed along the second virtual straight lines.